Meanwhile, the Pythagorean astronomical system proposed the Earth and Sun and a Counter-Earth rotate around an unseen "Central Fire". Though unclear if motivated by empirical observations, the concept of a Spherical Earth apparently first gained intellectual dominance in the Pythagorean school in Ancient Greece in the 5th century BC.
The basic elements of Ptolemaic astronomy, showing a planet on an epicycle (smaller dashed circle), a deferent (larger dashed circle), the eccentric (×) and an equant ( One important discovery made at different times in different places is that the bright planet sometimes seen near the sunrise (called Phosphorus by the Greeks) and the bright planet sometimes seen near the sunset (called Hesperus by the Greeks) were actually the same planet, Venus. Some traditions in Chinese cosmology proposed a surface to which planets and the Sun and Moon were attached another proposed they were free-floating.
Ancient models were typically geocentric, putting the Earth at the center of the universe, though the Vedic texts likely promote a spherical earth, which they refer to as bhugol (or भूगोल in Hindi and Sanskrit), which literally translates to spherical land or earth. Vedic texts proposed a number of shapes, including a wheel (flat) and a bag (concave). Early historic civilizations in Egypt, the Levant, pre-Socratic Greece, Mesopotamia, and Ancient China, recorded beliefs in a Flat Earth. Systematic astronomical observations were performed in many areas around the world, and started to inform cosmological knowledge. Many associated the classical planets (those visible with the naked eye) with deities. Prehistoric beliefs about the structure of the universe were highly diverse, often rooted in religious cosmology, and many are unrecorded. The Lunar phases allowed to measure time in longer periods than those of days, and predict the duration of seasons. The Moon was another body of immediate interest, because of its higher visual size. Even more, the dawn and sunset always take part at roughly the same points of the horizon, which helped to develop the cardinal directions. The Sun, however, was of immediate interest, as it generates the day-night cycle. The first humans had limited understanding of the celestial bodies that could be seen in the sky. On the left, summer on the right, winter. Illustration of Anaximander's models of the universe. Anything related to the Sun is called "solar" for example, stellar wind from the Sun is called solar wind. The planetary system that contains Earth is named the "Solar" System because the local star, the Sun, is named Sol, after the Latin word for Sun, "solis". The Solar System is one of many planetary systems in the galaxy. Robotic space probes, the Apollo program landings of humans on the Moon, and space telescopes have vastly increased human knowledge about atmospheric, geologic, and electromagnetic phenomena on other planets, giving rise to the new field of planetary science. Observations of Solar System bodies with other types of electromagnetic radiation became possible with radio astronomy, infrared astronomy, ultraviolet astronomy, X-ray astronomy, and gamma-ray astronomy. The composition of stars and planets was investigated with spectroscopy. Telescopic observations resulted in the discovery of more planets and asteroids and moons, and determination of the distances to some other stars. The collection of precise observations in the early modern period and the invention of the telescope helped determine the overall structure of the solar system and discover new planets and asteroids. Ancient astronomers were able to make geometric observations with various instruments. In ancient and medieval times, only the Sun, Moon, five classical planets and comets were visible to the naked eye, along with phenomena now known to take place in Earth's atmosphere, like meteors and aurora. This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust. This photograph is known as Pale Blue Dot.ĭiscovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". The streaks of light are diffraction spikes radiating from the Sun (off frame to the left). A photo of Earth (circled) taken by Voyager 1, 6.4 billion kilometers (4 billion miles) away.
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